Pneumatic launcher

ABSTRACT

A pneumatic launcher includes a number of chambers for holding a compressed gas and a valve for releasing the compressed gas into a firing chamber to fire a projectile. The firing valve may include a number of surfaces on which pressure acts to slide a sliding valve body between an open position and a closed position. The launcher may include a recess for preventing pressure from acting on one of those surfaces when the valve is in the closed position. A part of the sliding valve body may interact with adjacent parts to form a closed region ahead of the sliding valve body, in order to cushion motion of the sliding valve body. The launcher may have a breech and a breech pin shaped to create a desired gas flow within the firing chamber during firing. The breech may include a breech pin seal which seals between two faces oriented transverse to the axis of the launcher. The launcher barrel may have a number of ribs for improved stability and accuracy.

FIELD OF THE INVENTION

The invention relates to pneumatic launchers for launching projectiles,particularly but not exclusively to launchers for launching projectilesfor triggering avalanches.

BACKGROUND TO THE INVENTION

In various circumstances it may be desirable to trigger an avalanche,usually to prevent the build up of material which could form anuncontrolled avalanche at a later time.

Various methods of triggering avalanches have been used. Explosivecharges can be placed by hand, although this requires a worker to travelclose to the avalanche zone, which is both time consuming andpotentially dangerous. Therefore various methods of triggeringavalanches from a distance have been developed. Explosive charges can befired from a distance, for example using some form of launcher such as aHowitzer.

Such launchers include the “Avalauncher”, which delivers a projectileusing compressed gas. However, known pneumatic launchers perform poorlyin a number of areas. The launchers are generally inaccurate, whichleads to poor control of avalanche triggering. The launchers includevalves which are prone to wear and are relatively difficult to replace.

It is an object of the invention to provide an improved pneumaticlauncher, or at least to provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect the invention provides a pneumatic launcher having:

a firing chamber configured to hold a projectile to be fired, a wall ofthe firing chamber having one or more apertures therein forming a flowpath;a gas chamber for holding gas under pressure, the gas chambercommunicating via the flow path with the firing chamber; anda firing valve having an open position and a closed position, and beingconfigured to block the flow path in the closed position and, in theopen position, to allow gas under pressure to flow from the gas chambervia the flow path into the firing chamber, the firing valve including: asliding valve body having one or more operating surfaces angled withrespect to a movement direction of the sliding valve body, such thatpressure acting on the operating surfaces forces the valve body toslide; anda recess configured to receive, when the firing valve is in the closedposition, a part of the sliding valve body including at least a firstoperating surface such that pressure in a region outside the recess isprevented from acting on the first operating surface.

In a second aspect the invention provides a pneumatic launcher having:

a firing chamber configured to hold a projectile to be fired, a wall ofthe firing chamber having one or more apertures therein forming a flowpath;a valve chamber between the firing chamber wall and an outer valvechamber wall, the valve chamber communicating via the flow path with thefiring chamber;a gas chamber for holding gas under pressure and communicating with thevalve chamber; anda firing valve positioned within the valve chamber, the firing valvehaving an open position and a closed position, and being configured toblock the flow path in the closed position and, in the open position, toallow gas under pressure to flow from the valve chamber via the flowpath into the firing chamber, the firing valve including: a slidingvalve body having: an inner surface which engages with an outer surfaceof the firing chamber wall to close the flow path when the firing valveis in a closed position; one or more operating surfaces angled withrespect to a movement direction of the sliding valve body, such thatpressure acting on the operating surfaces forces the valve body toslide; and a protrusion extending outwards; and a valve wall positionedto the outside of the valve body and engaging with the protrusion, suchthat a pressure difference can be maintained between the regions on eachside of the protrusion.

In a third aspect the invention provides a pneumatic launcher having:

a firing chamber configured to hold a projectile to be fired, a wall ofthe firing chamber having one or more apertures therein forming a flowpath;a gas chamber for holding gas under pressure, the gas chambercommunicating via the flow path with the firing chamber; anda firing valve having an open position and a closed position, and beingconfigured to block the flow path in the closed position and, in theopen position, to allow gas under pressure to flow from the gas chambervia the flow path into the firing chamber, the firing valve including: asliding valve body having a range of movement and cooperating with apart of the launcher to form a substantially closed region ahead of themoving sliding valve body near an extremity of the range of movement,thereby cushioning the motion of the sliding valve body.

In a fourth aspect the invention provides a pneumatic launcher having:

a firing chamber configured to hold a projectile to be fired, a wall ofthe firing chamber having one or more apertures therein forming a flowpath;a gas chamber for holding gas under pressure, the gas chambercommunicating via the flow path with the firing chamber;a firing valve having an open position and a closed position, and beingconfigured to block the flow path in the closed position and, in theopen position, to allow gas under pressure to flow from the gas chambervia the flow path into the firing chamber; andwherein the firing valve is held in place by a fastening mechanism atone end of the valve and can be removed from the pneumatic launcher byreleasing the fastening mechanism and sliding the firing valve from thelauncher.

In a fifth aspect the invention provides a pneumatic launcher having:

a breech; anda breech plug configured to be inserted to close the breech duringfiring and to be removed from the breech to allow a projectile to beloaded into the launcher;wherein the breech plug extends into a firing chamber of the launcherand is shaped so as to produce a desired gas flow profile during firing,or is adapted to support an insert shaped so as to produce a desired gasflow profile during firing.

In a sixth aspect the invention provides a pneumatic launcher having:

a breech;a breech plug configured to be inserted to close the breech duringfiring and to be removed from the breech to allow a projectile to beloaded into the launcher; anda breech seal configured to seal between the breech and the breech plug,when inserted;wherein the breech seal seals between a first face on the breech and asecond face on the breech plug, the first and second faces beingsubstantially transverse to an insertion direction of the breech plug.

In a seventh aspect the invention provides a pneumatic launcherconfigured to project a projectile using gas pressure and having abarrel with one or more longitudinal ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a pneumatic launcher;

FIG. 2 is a cut away view of a valve section in a pneumatic launcher,showing the valve in an intermediate position;

FIG. 3 is a cut away view similar to FIG. 2, showing the valve in aclosed position;

FIG. 4 is a cut away view similar to FIG. 2, showing the valve in anopen position;

FIG. 5 is a cut away perspective view of the sliding valve body of thevalve section in FIG. 2;

FIG. 6 is a cut away perspective view of the valve wall of the valvesection in FIG. 2;

FIG. 7 is a cut away view of a pneumatic launcher breech assembly;

FIG. 8 is a perspective view of the breech assembly of FIG. 7;

FIG. 9 is a perspective view of one embodiment of a breech plug;

FIG. 10 shows the breech plug of FIG. 9, carrying a replaceable insert;

FIG. 11 is an enlarged view showing the breech plug seal;

FIG. 12 is a cut away perspective view showing the valve section andbreech assembly;

FIG. 13 is a cross-section of the pneumatic launcher barrel; and

FIG. 14 is a schematic diagram showing external valves and conduits usedto operate the launcher.

DETAILED DESCRIPTION

FIG. 1 shows a pneumatic launcher 1. The pneumatic launcher 1 mayinclude a base 2 which allows adjustment of the direction and elevationof the launcher 1. Adjustment of the direction may be achieved, forexample, using a turntable 3 driven by a handle 4 via a suitable gearmechanism 5. Adjustment of the elevation may be achieved, for example,using a hydraulic ram 6. The base 2 includes a number of supports 7,which support the main part of the pneumatic launcher 1. Thus, the base2 functions to support and direct the launcher 1. Many different typesof base or support may be used, or indeed the launcher may be usedwithout a base or support.

The pneumatic launcher 1 includes a number of gas chambers 10, 11, 12for holding a compressed gas before the launcher is fired. Thesechambers may be formed in any suitable manner, so long as they arecapable of withstanding the required pressures. Before firing, thechambers receive compressed gas from an external source and hold thecompressed gas until firing.

The chambers 10, 11, 12 communicate via conduits 13, 14, 15 with a valvesection 16, which is described in detail below. The valve section 16 inturn communicates with a barrel 17. The back of the valve section 16receives a breech assembly 18, which again is described in detail below.

In use, a projectile is loaded into a firing chamber in the valvesection 16, through the breech assembly 18. The breech is then closed.The valve contained in the valve section 16 is operated to releasecompressed gas from the chambers 10, 11, 12 into the firing chamber,forcing the projectile from the firing chamber through the barrel 17.

FIG. 2 is a cutaway view of the valve section 16. The valve section 16is of generally cylindrical construction. The valve section 16 includesa barrel end 20 and a breech end 21. The breech end 20 is configured toreceive the barrel 17 (see FIG. 1), while the breech end 21 receives thebreech assembly 18 (see FIG. 1).

The valve section 16 includes a number of apertures 23, 24 whichcommunicate with the conduits 13, 15 shown in FIG. 1. A further aperturewhich communicates with the conduit 14 of FIG. 1 is also provided but isnot shown in FIG. 2. The valve section 16 also includes a valve chamber25 communicating with the apertures 23, 24 formed in an outer wall ofthe valve chamber. The valve chamber 25 also communicates via apertures26, 27 with a firing chamber 28. The firing chamber 28 holds aprojectile before firing and, in the assembled pneumatic launcher,communicates with the barrel 17.

Thus, a flow path is established from the chambers 10, 11, 12 throughconduits 13, 14, 15 and apertures 23, 24 to the valve chamber 25. Theflow path extends from the valve chamber 25 via apertures 26, 27 to thefiring chamber 28.

A firing valve operates to open and close this flow path and may besituated within the valve chamber. In a closed position, the firingvalve obstructs the apertures 26, 27, such that compressed gas cannotflow from the valve chamber 25 into the firing chamber 28.

The firing valve may be formed as follows. A sliding valve body 30 maybe arranged with its inner surface 31 against the outer surface of thewall 32 of the firing chamber 28. The sliding valve body 30 slides alongthe length of the valve section 16 between a closed position (shown inFIG. 3) and an open position (shown in FIG. 4).

In the closed position (see FIG. 3) the sliding valve body 30 obstructsthe apertures 26, 27, preventing flow of compressed gas from the valvechamber 25 to the firing chamber 28. In the open position (see FIG. 4),the sliding valve body is positioned out of the way, such thatcompressed gas can flow freely from the valve chamber 25 to the firingchamber 28.

The sliding valve body 30 may be shaped to include a number of operatingsurfaces 33, 34, 35, 36, 37. Each operating surface is oriented at anangle to the direction of motion of the sliding valve body 30 (i.e. eachoperating surface is non-parallel to the direction of motion). Thereforepressure acting on each operating surface 33-37 creates a force tendingto cause sliding motion of the sliding valve body 30. Motion of thesliding valve body 30 may be controlled entirely by the action of gaspressure on these operating surfaces 33-37, as described below.

The firing valve also includes a valve wall 40, which may be positionedto the outside of the sliding valve body 30. The sliding valve body 30includes a protrusion 41, an outside surface of which engages with aninside surface of the valve wall 40. This means that a pressuredifference can be maintained between a region 42 on a first side of theprotrusion 41 (where pressure acts on the operating surface 33) and atrigger chamber 43 on a second side of the protrusion 41 (where pressureacts on the operating surface 34). The chamber 43 communicates with theoutside of the valve section 16 via a flow path 44.

FIG. 5 is a perspective cut away view of the sliding valve body 30,while FIG. 6 is a similar view of the valve wall 40. Note that theL-shaped end section 45 of the valve wall 40 consists of a number ofprotrusions 46 as shown in FIG. 6, rather than the continuous wall whichcould be incorrectly inferred from FIGS. 2 to 4.

The operation of the firing valve over a complete firing cycle will nowbe described with reference to FIGS. 2 to 4.

The valve chamber 25 begins in an unpressurised state. Pressure isintroduced via the flow path 44 into the trigger chamber 43, acting onthe operating surfaces 34, 35 to force the sliding valve body 30 intothe closed position.

The valve section 16 includes a recess 50, which is configured toreceive part of the sliding valve body 30, when the firing valve is inthe closed position. FIG. 3 shows a part 51 of the sliding valve body 30situated within the recess 50. In the closed position, pressure in thevalve chamber 25 does not act on a first operating surface 37, situatedat an end of the sliding valve body. Preventing pressure from acting onthis surface contributes to the stability of the closed position, sincethe pressure acting to force the sliding valve body 30 towards the openposition is lessened.

With the firing valve in the closed position shown in FIG. 3,pressurised gas is introduced into the chambers 10, 11, 12 and thereforeinto the valve chamber 25. This pressurised gas may be drawn from thesame source used to pressurise the trigger chamber 43. Even though thepressure in the valve chamber increases, acting on the operating surface33, the combined area of the surfaces 34, 35, 36 is sufficient to createa force holding the sliding valve body 30 in the closed position.

When the chambers 10, 11, 12 and the valve chamber 25 have beensufficiently pressurised, and an operator wishes to fire the pneumaticlauncher, the pressure in the chamber 43 is released (preferablysuddenly) to the outside of the valve section 16 via the flow path 44.The pressure in the trigger chamber 43 is now much lower than thepressure acting to force the sliding valve body 30 towards the openposition. The sliding valve body 30 therefore moves rapidly from theclosed position to the open position, allowing compressed gas to flowfrom the valve chamber 25 and chambers 10, 11, 12 into the firingchamber 28 to fire a projectile.

The motion of the sliding valve body is rapid. This is beneficial forthe firing of the pneumatic launcher 1, since it allows a rapid releaseof pressurised gas into the firing chamber 28. However, such rapidmotion tends to damage the mechanism of the firing valve, resulting in ashort lifetime of these components and/or a lack of reliability.Therefore, the valve section 16 is designed to cushion the motion of thesliding valve body 30 so as to reduce any damage caused to the valvecomponents.

During firing, the sliding valve body 30 moves from the closed positionof FIG. 3 through the intermediate position shown in FIG. 2 to the openposition shown in FIG. 4. In the position of FIG. 4, the end 53 of thesliding valve body 30 enters a narrowed passage 54 and the passage 54 isdimensioned to cooperate with the end 53 of the sliding valve body 30.This creates a substantially closed region 55 ahead of the protrusion 41of the advancing sliding valve body 30, near the end of its range ofmovement. This closed region 55 cushions or slows the motion of thesliding valve body 30, since the air within that region cannot escape,or cannot escape fast enough to allow the sliding valve body 30 to reachthe end of its range of motion unchecked.

A similar effect may be used to cushion motion of the sliding valve body30 from the open position to the closed position at the start of thefiring cycle. For example, a similar closed region could be createdusing the recess 50. Alternatively, the pressure introduced through theflow path 44 could initially be fairly low, so that motion of thesliding valve body 30 into the closed position is relatively gentle.

The outer wall 57 of the valve chamber 25 is formed with an end plate 58for mounting of the firing valve into the valve chamber. A fasteningmechanism, which may be a top plate 59 is used to secure the valve wall40 to the end plate 58. A number of fasteners, for example threadedscrews, engage with cooperating apertures 60 in the top plate 59, valvewall 40 and end plate 58. The top plate may also be shaped to supportthe barrel in the assembled launcher.

Other fastening mechanisms may also be suitable. However, it ispreferred that the fastening mechanism should be situated at one end ofthe valve section 16, such that when the fastening mechanism is removedthe firing valve (including the sliding valve body 30 and the valve wall40) can be removed by sliding it from the end of the valve section 16.

The valve section 16 also includes a bottom plate 62 situated at thebreech end 21 and configured to receive a breech assembly as describedbelow.

Finally, the valve section 16 includes a number of seals positioned toprevent the undesired flow of gas within the valve section. FIGS. 2 to 4show the grooves provided to receive the seals, which may be o-ringsformed from rubber, composite material or any other suitable material.

Thus, referring to FIG. 4, a groove 63 is provided in the outer surfaceof the projection 41. The seal contained in this groove restricts gasflow between the first side 42 and the second side 43 of the projection41. A seal 64 is provided between the outer surface of the firingchamber wall 32 and the inner surface of the sliding valve body 30.

A further seal 65 is provided near the end 51 of the sliding valve body30, in order to seal within the recess 50, preventing pressure in thevalve chamber 25 from acting on the first operating surface 37. Thisseal is carried on the sliding valve body, for ease of replacement.However, a similar seal could be provided in or near the recess 50. Twoor more seals could be used to perform this function.

The above seals are all seals provided between moving components.

Furthermore, seals are provided between fixed components where thosecomponents lie against each other in the assembled valve section 16.These include a seal 67 between the outer wall 57 of the valve chamberand the bottom plate 62; and seals 68, 69, 70 at the joins between theouter wall 57 of the valve chamber, valve wall 40 and top plate 59.

FIG. 7 shows the breech assembly 18 mounted to the bottom plate 62. Thebreech assembly 18 includes a backplate 75 which is secured to thebottom plate 62 by a number of fasteners. In the embodiment shown, thebackplate 75 and bottom plate 62 include a number of apertures 76 forreceiving threaded screws.

The breech assembly 18 also includes a locking ring 77 which rotatesabout the axis of the breech assembly 18. A locking handle 78 is mountedto the locking ring 77 to enable a user to operate the locking ring.

Finally, the breech assembly 18 includes a breech plug 79, which can beremovably inserted and locked into the breech by the locking ring 77.The breech plug can be removed for loading of a projectile into thefiring chamber and then inserted to close the breech during firing.

FIG. 8 is a perspective view of the breech assembly 18 mounted to thebottom plate 62. This view shows the cooperating shapes of the breechplug 79 and backplate 75. In use, the breech plug 79 can be insertedsuch that the lugs 80 situated on shoulders 81 pass through thecooperating aperture 82 in the backplate 75. The inner surface (notshown) of the locking ring 77 is shaped to allow the lugs 80 to passbeyond the locking ring 77 when the locking ring is in an open position.The locking ring can then be rotated to a locked position, in which theinner surface of the locking ring 77 engages with the lugs 80, lockingthe breech plug in place.

The breech plug 79 includes a protrusion 85 which sits within the firingchamber 28, in order to position a projectile for firing. The breechplug 79 may also be shaped appropriately, so as to achieve desired flowcharacteristics within the firing chamber 28. This may be achievedeither by shaping the breech plug 79, or by use of a shaped insert.

FIG. 9 is a perspective view of an alternative breech plug whichincludes a shaft 90 having a removable collar 91. FIG. 10 shows thebreech plug of FIG. 9, with a removable, shaped insert 92 arranged onthe shaft 90 and held in place by the collar 91 and fastener 93.

The shape of the breech plug 79, or the shape of the removable insert 92can be adapted for any desired purpose, such as altering the range ofthe pneumatic launcher, or adapting the pneumatic launcher for differenttypes of projectiles.

Furthermore, the breech plug operates to close or seal the breech duringfiring. For this purpose, a seal 95 may be provided, preferably betweenthe breech plug and the bottom plate 62. Preferably, the seal 95 issituated between two surfaces which lie against each other in a planesubstantially transverse to the axis of the breech assembly 18 (wherethe axis of the breech assembly lies along an insertion direction of thebreech plug). This orientation of the seal 95 provides improvedperformance over prior systems, in which a seal has been providedbetween circumferential faces. The seal 95 may be formed from rubber,composite or any other suitable material.

FIG. 11 is an enlarged view of the breech plug 79 and bottom plate 62(in which the backplate 75 and locking ring 77 are not shown). This viewclearly shows the position of the seal 95.

FIG. 12 is a cutaway perspective view of the valve section 16, with thebreech plug 79 in place. Again, the backplate 75 and locking ring 77 arenot shown in this view.

FIG. 13 is a cross-section of the barrel 17. The barrel 17 includes agenerally cylindrical bore 100, through which the projectile is fired.However, the barrel also includes a number of ribs 101, which providegreater rigidity to the barrel 17 without requiring a great deal ofadditional weight. The ribs may be external ribs. This improved rigidityprovides significantly increased accuracy.

FIG. 14 is a schematic diagram showing the various external valves andconduits used to operate the launcher. Pressurised gas, preferably drynitrogen, is held in a tank 105. This tank is connected by a conduit 106with a three-way valve 107. In one position this valve 107 operates tofeed pressurised gas into the trigger chamber 43 in the valve section 16through conduit 108 in order to close the firing valve. In a secondposition this valve 107 operates to feed gas through conduit 109 intothe three gas chambers 10, 11, 12 to pressurise those chambers. Aone-way check valve 110 allows gas to flow from the conduit 109 into theconduit 108 but does not allow gas to flow in the opposite direction.

The chamber 43 is also connected via conduit 112 with a safety valve 113and a trigger valve 114. The safety valve is to be closed whenever thebreech is open, and sensors and the like may be used to ensure that thisis the case. When the breech is closed, the safety valve 113 may beopened and the launcher may be fired by opening the trigger valve 114 torelease the pressure in the trigger chamber 43 to the atmosphere.

Finally, various sensors and safety devices may be provided. Pressurerelease or safety valves 115, 116 may be provided, and pressure gauges118 may be connected as required.

The gas chambers may be pressurised for firing to a pressure in therange about 40 to 600 pounds per square inch (psi), preferably in therange 100 to 400 psi. the pressure chosen may depend on the desiredrange as well as the nature of the projectile to be fired.

The firing chamber wall, sliding valve body, valve wall and the outerwall of the valve chamber may all be of generally cylindricalconstruction. This provides for ease of manufacture and alignment of theparts. In the assembled launcher, these parts may be arrangedsubstantially coaxially.

The outer valve chamber wall, bottom plate, top plate, valve wall,firing chamber wall, sliding valve body, breech assembly, breech plugand barrel may all be formed from steel or any other suitable material.

The pneumatic launcher 1 has been described in general terms. However,while the launcher is likely to have many and varied applications, it isexpected to be particularly applicable to launchers used for triggeringavalanches. Such launchers generally fire a projectile having anexplosive charge which detonates on or near a slope to trigger anavalanche.

The design of the valve section 16 provides improved reliability and alonger lifetime for the various components. Furthermore, the valvesection 16 is easily disassembled for removal or replacement of thefiring valve.

While the present invention has been illustrated by the description ofthe embodiments thereof, and while the embodiments have been describedin detail, it is not the intention of the Applicant to restrict or inany way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative apparatus andmethods, and illustrative examples shown and described. Accordingly,departures may be made from such details without departure from thespirit or scope of the Applicant's general inventive concept.

1. A pneumatic launcher having: i. a firing chamber configured to hold aprojectile to be fired, a wall of the firing chamber having one or moreapertures therein forming a flow path; ii. a gas chamber for holding gasunder pressure, the gas chamber communicating via the flow path with thefiring chamber; and iii. a firing valve having an open position and aclosed position, and being configured to block the flow path in theclosed position and, in the open position, to allow gas under pressureto flow from the gas chamber via the flow path into the firing chamber,the firing valve including: a) a sliding valve body having one or moreoperating surfaces angled with respect to a movement direction of thesliding valve body, such that pressure acting on the operating surfacestends to force the valve body to slide; and iv. a recess configured toreceive, when the firing valve is in the closed position, a part of thesliding valve body including at least a first operating surface suchthat pressure in a region outside the recess is prevented from acting onthe first operating surface.
 2. A pneumatic launcher as claimed in claim1 wherein the first operating surface is situated at an end of thesliding valve body.
 3. A pneumatic launcher as claimed in claim 1including one or more seals arranged to seal the recess around the partof the sliding valve body, when the firing valve is in the closedposition.
 4. A pneumatic launcher as claimed in claim 3 wherein the oneor more seals are positioned on the sliding valve body.
 5. A pneumaticlauncher as claimed in claim 1 wherein, when the firing valve is in theclosed position, pressure acting on the operating surfaces except thefirst operating surface, maintains the firing valve in the closedposition and wherein, on release of pressure from a trigger chamber,pressure acting on the operating surfaces causes the firing valve toopen.
 6. A pneumatic launcher as claimed in claim 1 further including avalve chamber between the firing chamber wall and an outer valve chamberwall, the valve chamber communicating via the flow path with the firingchamber and also communicating with the gas chamber, the firing valvebeing positioned within the valve chamber.
 7. A pneumatic launcher asclaimed in claim 6, wherein the sliding valve body includes: a) an innersurface which engages with an outer surface of the firing chamber wallto close the flow path when the firing valve is in a closed position;and b) a protrusion extending outwards; and wherein the launcherincludes a valve wall positioned to the outside of the valve body andengaging with the protrusion, such that a pressure difference can bemaintained between the regions on each side of the protrusion.
 8. Apneumatic launcher as claimed in claim 7 configured to enable a suddenreduction in pressure on one side of the protrusion, such that pressureacting on the operating surfaces on the other side of the protrusionmoves the sliding valve member to the open position.
 9. A pneumaticlauncher as claimed in claim 1 wherein the sliding valve body has arange of movement and cooperates with a part of the launcher to form asubstantially closed region ahead of the moving sliding valve body nearan extremity of the range of movement, thereby cushioning the motion ofthe sliding valve body.
 10. A pneumatic launcher as claimed in claim 1wherein the firing valve is held in place by a fastening mechanism atone end of the valve and can be removed from the pneumatic launcher byreleasing the fastening mechanism and sliding the firing valve from thelauncher.
 11. A pneumatic launcher as claimed in claim 10 wherein thefastening mechanism is a top plate which also supports a barrel.
 12. Apneumatic launcher as claimed in claim 1 wherein the sliding valve bodyand the firing chamber wall are formed as substantially cylindricalcoaxial elements.
 13. A pneumatic launcher as claimed in claim 1including a plurality of seals for sealing between the sliding valvebody and adjacent elements to prevent undesired flow of gas.
 14. Apneumatic launcher as claimed in claim 1, including: i. a breech; andii. a breech plug configured to be inserted to close the breech duringfiring and to be removed from the breech to allow a projectile to beloaded into the launcher; wherein the breech plug extends into thefiring chamber of the launcher and is shaped so as to produce a desiredgas flow profile during firing, or is adapted to support an insertshaped so as to produce a desired gas flow profile during firing.
 15. Apneumatic launcher as claimed in claim 1, including: i. a breech; ii. abreech plug configured to be inserted to close the breech during firingand to be removed from the breech to allow a projectile to be loadedinto the launcher; and iii. a breech seal configured to seal between thebreech and the breech plug, when inserted; wherein the breech seal sealsbetween a first face on the breech and a second face on the breech plug,the first and second faces being substantially transverse to aninsertion direction of the breech plug.
 16. A pneumatic launcher asclaimed in claim 1, including: i. a breech; ii. a breech plug configuredto be inserted to close the breech during firing and to be removed fromthe breech to allow a projectile to be loaded into the launcher; andiii. a locking ring configured to rotate between a first position inwhich the breech plug can be removed or inserted into the breech and asecond position in which the breech plug is locked into the breech forfiring.
 17. A pneumatic launcher as claimed in claim 1 having a barrelwith one or more longitudinal ribs.
 18. A pneumatic launcher as claimedin claim 1 configured to fire an avalanche-triggering projectile.
 19. Apneumatic launcher having: i. a firing chamber configured to hold aprojectile to be fired, a wall of the firing chamber having one or moreapertures therein forming a flow path; ii. a valve chamber between thefiring chamber wall and an outer valve chamber wall, the valve chambercommunicating via the flow path with the firing chamber; iii. a gaschamber for holding gas under pressure and communicating with the valvechamber; and iv. a firing valve positioned within the valve chamber, thefiring valve having an open position and a closed position, and beingconfigured to block the flow path in the closed position and, in theopen position, to allow gas under pressure to flow from the valvechamber via the flow path into the firing chamber, the firing valveincluding: c) a sliding valve body having: i. an inner surface whichengages with an outer surface of the firing chamber wall to close theflow path when the firing valve is in a closed position; ii. one or moreoperating surfaces angled with respect to a movement direction of thesliding valve body, such that pressure acting on the operating surfacestends to force the valve body to slide; and iii. a protrusion extendingoutwards; d) a valve wall positioned to the outside of the valve bodyand engaging with the protrusion, such that a pressure difference can bemaintained between the regions on each side of the protrusion.
 20. Apneumatic launcher as claimed in claim 19 configured to enable a suddenreduction in pressure on one side of the protrusion, such that pressureacting on the operating surfaces on the other side of the protrusionmoves the sliding valve member to the open position.
 21. A pneumaticlauncher as claimed in claim 19 wherein the sliding valve body has arange of movement and cooperates with a part of the launcher to form asubstantially closed region ahead of the moving sliding valve body nearan extremity of the range of movement, thereby cushioning the motion ofthe sliding valve body.
 22. A pneumatic launcher as claimed in claim 19wherein the firing valve is held in place by a fastening mechanism atone end of the valve and can be removed from the pneumatic launcher byreleasing the fastening mechanism and sliding the firing valve from thelauncher.
 23. A pneumatic launcher as claimed in claim 19 wherein thesliding valve body, the valve wall and the firing chamber wall areformed as substantially cylindrical coaxial elements.
 24. A pneumaticlauncher as claimed in claim 19, including: v. a breech; and vi. abreech plug configured to be inserted to close the breech during firingand to be removed from the breech to allow a projectile to be loadedinto the launcher; wherein the breech plug extends into the firingchamber of the launcher and is shaped so as to produce a desired gasflow profile during firing, or is adapted to support an insert shaped soas to produce a desired gas flow profile during firing.
 25. A pneumaticlauncher as claimed in claim 19, including: v. a breech; vi. a breechplug configured to be inserted to close the breech during firing and tobe removed from the breech to allow a projectile to be loaded into thelauncher; and vii. a breech seal configured to seal between the breechand the breech plug, when inserted; wherein the breech seal sealsbetween a first face on the breech and a second face on the breech plug,the first and second faces being substantially transverse to aninsertion direction of the breech plug.
 26. A pneumatic launcher asclaimed in claim 19, including: V. a breech; vi. a breech plugconfigured to be inserted to close the breech during firing and to beremoved from the breech to allow a projectile to be loaded into thelauncher; and vii. a locking ring configured to rotate between a firstposition in which the breech plug can be removed or inserted into thebreech and a second position in which the breech plug is locked into thebreech for firing.
 27. A pneumatic launcher as claimed in claim 19having a barrel with one or more longitudinal ribs.
 28. A pneumaticlauncher as claimed in claim 19 configured to fire anavalanche-triggering projectile.
 29. A pneumatic launcher having: i. afiring chamber configured to hold a projectile to be fired, a wall ofthe firing chamber having one or more apertures therein forming a flowpath; ii. a gas chamber for holding gas under pressure, the gas chambercommunicating via the flow path with the firing chamber; and iii. afiring valve having an open position and a closed position, and beingconfigured to block the flow path in the closed position and, in theopen position, to allow gas under pressure to flow from the gas chambervia the flow path into the firing chamber, the firing valve including:a) a sliding valve body having a range of movement and cooperating witha part of the launcher to form a substantially closed region ahead ofthe moving sliding valve body near an extremity of the range ofmovement, thereby cushioning the motion of the sliding valve body.
 30. Apneumatic launcher as claimed in claim 29 wherein the sliding valve bodyhas one or more operating surfaces angled with respect to a movementdirection of the sliding valve body, such that pressure acting on theoperating surfaces tends to force the valve body to slide; and whereinthe launcher includes a recess configured to receive, when the firingvalve is in the closed position, a part of the sliding valve bodyincluding at least a first operating surface such that pressure in aregion outside the recess is prevented from acting on the firstoperating surface.
 31. A pneumatic launcher as claimed in claim 30wherein, when the firing valve is in the closed position, pressureacting on the operating surfaces except the first operating surface,maintains the firing valve in the closed position and wherein, onrelease of pressure from a trigger chamber, pressure acting on theoperating surfaces causes the firing valve to open.
 32. A pneumaticlauncher as claimed in claim 29 wherein the sliding valve body and thefiring chamber wall are formed as substantially cylindrical coaxialelements.
 33. A pneumatic launcher as claimed in claim 29 configured tofire an avalanche-triggering projectile.
 34. A pneumatic launcherhaving: i. a firing chamber configured to hold a projectile to be fired,a wall of the firing chamber having one or more apertures thereinforming a flow path; ii. a gas chamber for holding gas under pressure,the gas chamber communicating via the flow path with the firing chamber;iii. a firing valve having an open position and a closed position, andbeing configured to block the flow path in the closed position and, inthe open position, to allow gas under pressure to flow from the gaschamber via the flow path into the firing chamber; and wherein thefiring valve is held in place by a fastening mechanism at one end of thevalve and can be removed from the pneumatic launcher by releasing thefastening mechanism and sliding the firing valve from the launcher. 35.A pneumatic launcher having: i. a breech; and ii. a breech plugconfigured to be inserted to close the breech during firing and to beremoved from the breech to allow a projectile to be loaded into thelauncher; wherein the breech plug extends into a firing chamber of thelauncher and is shaped so as to produce a desired gas flow profileduring firing, or is adapted to support an insert shaped so as toproduce a desired gas flow profile during firing.
 36. A pneumaticlauncher having: i. a breech; ii. a breech plug configured to beinserted to close the breech during firing and to be removed from thebreech to allow a projectile to be loaded into the launcher; and iii. abreech seal configured to seal between the breech and the breech plug,when inserted; wherein the breech seal seals between a first face on thebreech and a second face on the breech plug, the first and second facesbeing substantially transverse to an insertion direction of the breechplug.
 37. A pneumatic launcher configured to project a projectile usinggas pressure and having a barrel with one or more longitudinal ribs. 38.A pneumatic launcher as claimed in claim 37 wherein the ribs include oneor more external ribs.